Many different fields of application are known for solenoid valves in internal combustion engines. For instance, solenoid valves are used both in pneumatic and in hydraulic circuits of vehicles, such as, for example, in brake systems, operating systems or also injection systems. They can also be used for pressure control in pneumatic actuators or, for example, as circulation-type slide valves of turbochargers. Depending on the respective application, these solenoid valves are designed either as on/off valves or as control valves. Particularly when using such valves as regulation or control valves, it is important to prevent a coaxial offset of the armature in the magnetic circuit because this would cause radial forces having a negative influence on the desired axial forces.
A solenoid valve of the above type is described, for example, in DE 41 10 003 C1 and DE 42 05 565 C2. The described electropneumatic pressure transducer comprises a core screwed into a threaded bush wherein said threaded bush can also be integral with the return plate. The opportunity to perform a defined adjustment of the iron core makes it possible to eliminate all influences of mechanical and electromagnetic tolerances. Additional fine-adjustment is rendered possible by arranging, in the core, a further core which can extend into a recess of the armature. The armature is supported in one or several bearings which in turn are arranged in a steel bush, said steel bush being provided in the coil carrier. In such an arrangement, alignment errors between the components for guiding the anchor or fixing the core will cause a non-negligible coaxial error of the armature relative to the core. Deformation of the coil carrier as caused by winding the coil during assembly of the electromagnetic circuit, or by the process of injection-molding the housing, will also result in a further increase of the coaxial error.
A further embodiment of a solenoid valve for control purposes is described in DE 101 46 497 A1. In this valve, a hollow cylindrical armature is supported directly in a correspondingly configured coil carrier which thus serves as a slide bearing for the armature, and which is made of injection-molded plastic. The core is fastened in the housing by means of a connection nipple and extends into the area of the coil carrier, thus serving at the same time as a further valve seat for a valve closure member which is connected to the armature. In such an arrangement, coaxial errors also cannot be avoided because the coil will be wound around the coil carrier after the injection-molding process.
A further possibility for avoiding a coaxial error is described in DE 20 2007 002 100 U1. In this electromagnetic actuator, a centering bush is provided, accommodating the bearing guide elements of the armature system as well as the iron core.
Due to the high expenditure for component parts and assembly, all of the above outlined approaches for avoiding a coaxial error, particularly in a solenoid valve with an adjustable core, will cause considerable costs.